Cores of the type made and used according to the invention are substantially represented by shaped bodies made of sand held together by a binder capable of bestowing on the core the characteristics of solidity necessary for its correct use.
In the present description, as likewise in the ensuing claims, the term “sand” is used with the meaning commonly attributed to such a term in foundry techniques, i.e., to indicate sand of any type and nature, as well as particulate materials equivalent to sand, hence with the exclusion of materials of finer grain size, commonly referred to as “powder”.
The term “binder” is understood as indicating any substance that can hold together, according to any physico-chemical mechanism, the grains of sand so as to ensure the necessary solidity of the core.
In the fabrication of said cores, it is common to resort to the solution which envisages blowing a flow of sand with associated thereto the binder or a precursor thereof inside a mould (i.e., core blowing). Once the mould has been filled, the mass of sand thus obtained is consolidated by activating, or else completing, the mechanism of intervention of the binder.
The above operation may involve heating the mass of sand that is in the mould—in the case of binders the mechanism of action of which is linked to heating—or else blowing in a catalyst or reagent (for example, an amine), which is designed to promote the intervention of the binder.
In more recent times, there has been proposed (see, for example, EP-B1-608926) a technique that envisages the use, as binder, of a protein, which is mixed to the sand in “hydrated” form, i.e., with the addition of water or equivalent humidifying agent.
The mechanism of intervention of said binder is hence linked to the possibility of removing the humidity present in the mixture of sand and protein blown into the mould. This result is normally obtained by passing a flow of hot and de-humidified aeriform through the mass of sand that is in the mould.
The techniques of fabrication of cores for foundry usually require the execution of other additional steps, which, however, are well known in the art and thus not described herein and not of specific importance for the purposes of the present invention.
In the solutions according to the known art, it is envisaged that the moulds (which are usually two, that are complementary to one another) that jointly define the moulding cavity of the core will be provided with ducts designed to function, respectively, as delivery ducts and extraction ducts of the aforesaid flow of aeriform.
Usually, said ducts present, in an area corresponding to their end facing the surface of the mould of the core, a gauze or filter designed to prevent, before the definitive consolidation of the core, the sand that composes it from accidentally penetrating the respective duct.
Broadly speaking, in the solutions according to the known art, the aforesaid ducts or channels for flow of aeriform are made in the (half) moulds so as to give rise to a flow of aeriform designed to traverse the sand core being formed in the mould cavity along a single principal direction.
This may be a vertical direction, in the case where the two half-moulds are superimposed on top of one another (according to the solution of use prevalent in the prior art), or else a horizontal direction (in the case where the two half-moulds are arranged alongside one another, according to another solution used in the known art).
The experience of use of said known solutions show, however, that these may be further improved in the areas of the possibility of speeding up the process of consolidation of the core entrusted to the flow of aeriform, also rendering more homogeneous the results obtained, when it is a matter of moulding cavities, and hence cores, of a particularly complex shape.